A structure disclosed, e.g., in Japanese Patent Laying-Open No. 2003-043554 (Patent Document 1) has been known as the above kind of shutter actuator device, and FIG. 4 shows a shutter actuator device similar to the disclosed device. This shutter actuator device includes a shutter actuator drive circuit 101, a shutter actuator 8 that is driven by shutter actuator drive circuit 101 to operate a shutter (not shown) and a coil current detection element 9 that detects a coil current IL of shutter actuator 8, and provides a coil current detection voltage VDET corresponding to a value of coil current IL to a coil current detection terminal DET of shutter actuator drive circuit 101.
Shutter actuator drive circuit 101 includes a Zener diode 131, a constant current supply 132 having opposite ends connected to Zener diode 131 and an internal power supply voltage VCC, respectively, resistances 133 and 134 arranged in series between a ground potential point and a connection point between Zener diode 131 and constant current supply 132, and a capacitor 135 arranged in parallel to resistance 134. Shutter actuator drive circuit 101 further includes an NPN bipolar transistor 136 that has a collector connected to a connection point (node N) between resistances 133 and 134, a base receiving an activation signal from an activation signal input terminal ST and a grounded emitter, a coil current control amplifier 115 receiving on its noninverting input terminal a voltage on node N, and receiving, on its inverting input terminal, coil current detection voltage VDET from coil current detection terminal DET for amplifying a difference between them, and an NPN bipolar transistor 119 having a base receiving an output voltage of coil current control amplifier 115, an emitter connected to coil current detection terminal DET and a collector connected to the other end of shutter actuator 8 via an output terminal OUT2.
Resistances 133 and 134 as well as capacitor 135 from a CR integrator. A power supply voltage VM for driving the actuator is connected to one end of shutter actuator 8 via an output terminal OUT1.
Shutter actuator drive circuit 101 operates as follows.
When the activation signal on activation signal input terminal ST attains a low level (i.e., when the shutter actuator device becomes active), a current of constant current supply 132 flows into the CR integrator formed of capacitor 135 and resistances 133 and 134. The CR integrator gradually raises the voltage on node N, and will maintain the raised voltage after the voltage becomes equal to a voltage obtained by dividing the constant voltage generated by Zener diode 131 by resistances 133 and 134. Coil current detection voltage VDET follows the voltage on node N, and therefore the current flowing through coil current detection element 9, i.e., coil current IL likewise follows it, rises to an upper limit value IMAX and will maintain it.
Coil current IL of shutter actuator 8 does not rapidly rise due to its dielectric properties. If the CR integrator were not used for controlling the rising of coil current IL, the time required for raising coil current IL to upper limit value IMAX would vary according to variations in actuator drive power supply voltage VM as illustrated by waveforms A and B in FIG. 5.
Waveform A occurs when actuator drive power supply voltage VM takes a maximum value. Waveform B occurs when actuator drive power supply voltage VM takes a minimum value. In shutter actuator drive circuit 101, a constant of the CR integrator is adjusted to increase coil current IL with a slight delay from waveform B so that the foregoing time is not affected by the variations in actuator drive power supply voltage VM.
Patent Document 1: Japanese Patent Laying-Open No. 2003-043554